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<title>NAS - Normbasierte AustauschSchnittstelle</title>
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<h1>NAS - ALKIS</h1>

<p>The NAS driver reads the NAS/ALKIS format used for cadastral data in Germany.
The format is a GML profile with fairly complex GML3 objects not easily read
with the general OGR GML driver.</p>

<p>This driver depends on GDAL/OGR being built with the Xerces XML parsing
library.</p>

<p>The driver looks for "opengis.net/gml" and one of the strings semicolon
separated strings listed in the option <b>NAS_INDICATOR</b> (which defaults to
"NAS-Operationen;AAA-Fachschema;aaa.xsd;aaa-suite") to
determine if a input is a NAS file and ignores all files without any matches.</p>

<p>In GDAL 2.3 a bunch of workarounds were removed, that caused the driver to
remap or ignore some elements and attributes internally to avoid attribute
conflicts (e.g. <i>zeigtAufExternes</i>).  Instead it now takes the
<b>NAS_GFS_TEMPLATE</b> option, that makes it possible to cleanly map element
paths to feature attributes using a GFS file like in the GML driver.  Multiple
geometries per layer are also possible (eg.  ax_flurstueck.objektkoordinaten
next to the regular wkb_geometry).

<p>A <a href="https://github.com/norBIT/alkisimport/blob/master/alkis-schema.gfs">GFS template</a> and
a corresponding <a href="https://github.com/norBIT/alkisimport/blob/master/alkis-schema.sql">PostgreSQL schema</a>
of the full NAS schema are part of <a href="http://www.norbit.de/68/">norGIS ALKIS-Import</a>
(also featuring a shell script and PyQt frontend which ease the import).  The
two files were generated using <a href="https://github.com/norBIT/xmi2db/">xmi2db</a>
(fork of <a href="https://github.com/pkorduan/xmi2db">xmi2db</a>) from the
official application schema.</p>

<p>New in 2.3 is also the option <b>NAS_NO_RELATION_LAYER</b> that allows to
disable populating the table <i>alkis_beziehungen</i>.  The information found
there is redundant to the relation fields also contained in original
elements/tables.  Enabling the option also makes progress reporting
available.</p>

<p>This driver was implemented within the context of the
<a href="http://trac.wheregroup.com/PostNAS">PostNAS project</a>,
which has more information on it's use and other related projects.</p>

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